Preparation of washed emulsions and gelatin derivatives employed as peptizers in their preparation



United States Patent 2,956,880 PREPARATION OF WASHED EMULSIONS. AND

Patented Oct. 18, 1960 ice anhydride per 100 parts of gelatin sufiicientphthalyl content is imparted thereto to be suitable for coagu- GELATINDERIVATIVES ENIPLOYED AS PEP 5 TIZERS IN THEIR PREPARATION i John Gates,Jr., and Paul E. Miller, Rochester, N.Y., assignors to Eastman Kodak,Company, Rochester,. N.Y., a corporation of New Jersey 4 No Drawing.Filed ran. 4, 1957, Ser. No. 632,422-

2Claims. or. 96-94) This invention relates to the preparation of newgelatin derivatives and the use of those derivatives in the coagulationwashing of photographic emulsions in the presence of heavy metal salts.

It is often desirable in the preparation of photographic emulsions thata small amount of a heavy metal salt be incorporated therein to impartdesired characteristics to the emulsion. For instance, emulsions aresometimes prepared with cadmium salts, such as cadmium chloride,

therein which has the elfect of restricting the grain growth in thepreparation of the silver halide and alsov acts as an anti-foggant inthe photographic emulsion. The presence of other heavy metal salts suchas iron, lanthanum, zinc, aluminum, nickel or chromium, may be desirablein emulsion preparations. coagulation washing of photographic emulsionshave been described in U.S. Patents Nos. 2,614,928 and 2,- 614,931. Inthose methods gelatin derivatives are employed which make possible theconversion of the sil-.

ver halide dispersion to a coagulated form upon adjustment of the pHthereof. However, when heavy metal salts are present in the emulsion,coagulation of the peptizer may occur at normal pH values. A method forthe coagulation washing of emulsions is described in U.S. applicationSerial No. 406,061 of Russell in which those salts are added to causecoagulation to occur. This ver halide in the presence of the heavy metalsalt to form a silver halide dispersion and therefore is not adapted foruse in cases where the presence of the heavy metal salt is desirable inthe silver halide formation operation.

One object of our invention is to provide a method of coagulationwashing of silver halide dispersions in which heavy metal salts havebeen employed in their preparation. Another object of our invention isto provide gelatin derivatives which are useful in such a process. Astill further object of our invention is to provide a procedure forpreparing those gelatin derivatives. A still further object of ourinvention is to provide a coagulation method in which the coagulationoccurs at a pH of 3.0-4.5. Other objects of our invention will appearherein.

We have found that a phthalated gelatin which contains 3-10 percent of alower fatty acid radical therein such as acetyl, propionyl or the like,may be prepared by reacting phthalyl gelatin with lower fatty acidanhydride or by reacting upon gelatin simultaneously with phthalicanhydride and the lower fatty acid anhydride. We have found that silverhalide dispersions in which gelatin derivatives of that type arepresent, are readily coagulated upon lowering of the pH thereof eventhough soluble heavy metal salts are present in the silver halidedispersion. We have found that by our procedure washed silver halideemulsions having a heavy metal salt content may be prepared by acoagulation method. The amount of phthalyl added to the gelatin may varybut the gelatin is reacted with five parts of phthalic Methods for thelation washing as described herein.

.Whena gelatinv derivative, such as a phthalic anhydride derivative of;gelatin prepared by. reacting upon 100 parts. offgelatinwith five, partsof phthalic anhydride,

' is employed as the peptizer for silver halidein a dispersioncontaining cadmium chloride or the like, this dispersion coagulates at apH between 7.0 and 4.5. If on the other hand a gelatin derivativecontaining both phthalyl andacetyl is employed and the silver halide isprepared invthe presence of cadmium chloride, no coagulation occurswithin this pH range and to obtain coagulation it is necessary to reducethe pH such as to 3.0-4.5. .This holds true with gelatin derivativeshaving various phthalyl contents. For instance, if the gelatin has beenreacted with phthalic anhydride in the amount of five :parts, sevenparts or ten parts thereof per 100 parts of gelatin, the productsobtained when used as peptiz'e'rs will result in coagulation of thesilver halide dispersion when cadmium chloride is added at a usual PH;Whereas if a small percentage of lower fatty acid radical ispresent-therein, such as 5 percent, 8 percent or 10 percent acetyl, thedispersion does not coagulate when heavy metal salt is present therein.In the latter case, it is onlyrwhen the pH is reduced to a value withinthe range of. 3.0-4.5 that coagulation occurs.

The coagulate may be washed any number of times at the lowered pH andmay be redispersed in water having a pH in the vicinity of 7.0 to form awashed emulp) sion having a contentof heavy metal salt therein.Sometimes it is desirable .to add heavy metal salts as coating addendato emulsions just prior to coating. In those cases with the previouslymentioned types of gelatin derivatives used as peptizers, there isdanger of haze developing in the emulsion unless a considerablequanmethod, however, precludes the preparation of the siltity of gelatinwas employed as the carrier for the silver halide. By using a peptizerin accordance with our invention, any such haze eflect is avoided.

The following examples illustrate the preparation of gelatin derivativesuseful for preparing washed emulsions in accordance with our invention:

Example 1 100 parts of 5 percent phthalyl gelatin was plumped for 1 hourin 700 parts of water. The mass was stirred at 110 F. whereupon thegelatin derivative melted. The

pH was adjusted to 9.5 with 20 percent aqueous sodium hydroxide.Eighteen parts of propionic anhydride was added dropwise to the stirredmass over a 10-minute period while keeping the pH at 9.5. When the addi-"tion of propionic anhydride had been completed, the

pH was lowered to 6.0 with 6-N-sulfuric acid. The gelatin derivativethus obtained was chilled, washed and dried in the usual manner. Agelatin derivative having both propionyl and phthalyl groups wasobtained. When a solution of this gelatin derivative was mixed with acadmium chloride solution, no interaction took place, but a coagulateformed upon dropping the pH thereof to 3.8.

- Example 2 Example 3 A gelatin derivative was prepared by the sameprocedure as described in Example 1 except that 600 parts of percentphthalyl gelatin was: employed in 2400"parts of water and this solutionwas treated with; l20 parts of acetic anhydride at a pH of 9.5. Thernass was then adjusted to a pH of 6.0: and the gelatin derivativeobtained' was chilled, washed and dried in the usual-manner; a

The acetyl phthalyl gelatin did not interact with cadmium chloridesolution at that pH' but coagulated when the pH was reduced'to 3.5.

Example 4 200 parts of: gelatin were plumped in 800: parts of' water anda. solution was obtained by heating to 110 F- with gentle agitation. ThepH was adjusted to 9.5 with 20 percent aqueous sodium hydroxide and 20parts of finely divided phthalic anhydride. was added. The pH was heldat 9.5 by the occasional addition of alkali. At the completion of thereaction, 25 parts of acetic anhydride was added dropwise to the stirredsolution while maintaining the pH' at 9.5. The pH was then adjusted to6.0 with 6N-sulfuric acid and the solution was chilled, noodled andwashed and the product was dried in a conventional manner. A gelatinderivative containing phthalyl and acetyl groups was obtained.

Example 5 Example 6 Into a container with temperature control was put asolution with the following composition:

Parts Potassium bromide 165 Potassium iodide 5 Acetyl phthalyl gelatinprepared using 7 parts of phthalic anhydride per 100 of gelatin andhaving an acetyl content of 10% 5.0.5 Cadmium chloride 7.5

Water 1700 In another container a filtered solution consisting of 200parts. of silver nitrate and 2000 parts of water was placed. The silvernitrate solution was placed. in a separating funnel at a temperature of72 C. from which it was run, slowly, through a calibrated nozzle intothe first container. The contents of the latter were kept at atemperaturev of 70 C. and in constant motion by a mechanical stirrerduring the precipitation and ripening An emulsion was prepared in theabsence of cadmium chloride using the same amount of phthalyl gelatinderivative, which derivative had'no acetyl therein. The pH of therespective emulsions was lowered by the addition of sulfuric acid to thepoint at which the Silver halide dispersions coagulated, the motherliquor was decanted off in each case and the silver halide dispersionwas washed twice at 20 C. There was then added to the mass sufiicient.gelatin in distilled water to form a satisfactory emulsion upon.stirring the mass at 40 C. Ammonia was added to bring the emulsion pH to6.5 and stirring was continued until all of the solid matter wascompletely dispersed.

The two emulsions thus prepared were coated in the conventional mannerupon suitable film base, exposed of a second using an Eastman 1Bsensitometer with a 500-watt lamp at 3000 K. and developed 4 minutes inKodak developer 13-19. The emulsion inwhich the cadmiunr chloride wasemployed, had a similar speed and a higher gamma value than that inwhich .the cadmium chloride was omitted. The. addition of cadmiumchloride to the dispersion prepared using nonacetylated phthalyl- FramePatent No. 2,525,753 is a typical example of the.

preparation of the phthalylated gelatin. By this method. sufficientphthalyl is imparted to the. gelatin to impart acid-reversiblecharacteristics thereto- The amount of fatty acid radical imparted tothe gelatin to give the desired efiect in accordance with our inventionis 3 per cent upto 10 percent or even more if esterifiable groups:

are present in the gelatin. The amount of cadmium.

chloride or other heavy metal salt which is present in.

the. emulsion in accordance with our invention may be from A percent upto 4 percent based on the weight of the gelatin employed. Thecoagulation values for the.

silvere halide dispersions which are coagulated in accordance with ourinvention are all. found. within the range of 3-45. The acetyl phthalylgelatins prepared in ac-- cordance with our invention are obtainedeither by acylating phthalyl gelatin or by reacting upon gelatin. withboth phthalic anhydride and lower fatty acid. anhydride simultaneously'.The gelatin which is employed is prefarably of photographic grade.

We claim:

1. A. method of preparing a silver halide dispersion.

adapted to be coagulation washed even in the presence of heavy metalsalts which comprises reacting alkali metal halide With silver nitratein an aqueous solution containing the soluble. salt of a polyvalentheavy metal and as the. peptizing agent therein gelatin lower alkanoatephthalate. which. is; the reaction product of a lower alkanoic acid,anhydride and phthalic anhydride with gelatin in anhydride and parts byweight of the gelatin.

2. A method of preparing washed silver halide photographic emulsionwhich comprises mixing in the presence of cadmium chloride a solution ofsilver nitrate and as.

a peptizer a solution of alkali metal halide with a gelatin acetatephthalate which is a reaction product of acetic acid anhydride andphthalic anhydride with gelatin in the ratio of 5 to 20 parts by weightof acetic acid anhydride, 3 to 10 parts by weight of phthalic anhydrideand 100 parts by weight of gelatin, thereby forming a silver halidedispersion, adding acid to the dispersion to reduce the pH of themass toa. value within the pH range of 3-4.5

to coagulate the solids therein and subsequently dispersing thecoagulate in a vehicle for the silver halide under non-coagulatingconditions.

References Cited in the file of this patent UNITED STATES PATENTS2,423,773 Hart et al. July 8, 1947 2,494,041 Frame Jan. 10., 19502,592,263 Frame Apr. 8, 1952' 2,614,928 Yutzy et al Oct. 21, 19522,614,929 Yutzy et a1. Oct. 21, 1952'

1. A METHOD OF PREPARING A SILVER HALIDE DISPERSION ADAPTED TO BECOAGULATION WASHED EVEN IN THE PRESENCE OF HEAVY METAL SALTS WHICHCOMPRISES REACTING ALKALI METAL HALIDE WITH SILVER NITRATE IN AN AQUEOUSSOLUTION CONTAINING THE SOLUBLE SALT OFR A POLYVALENT HEAVY METAL AND ASTHE PEPTIZING AGENT THEREIN GELATIN LOWER ALKANOATE PHTHALATE WHICH ISTHE REACTION PRODUCT OF A LOWER ALKANOIC ACID ANHYDRIDE AND PHTAHLICANHYDRIDE WITH GELATIN IN THE RATIO OF 5 TO 20 PARTS BY WEIGHT OF THELOWER ALKANOIC ACID ANHYDRIDE, 3 TO 10 PARTS BY WEIGHT OF THE PHTHALICANHYDRIDE AND 100 PARTS BY WEIGHT OF THE GALATIN.